Scheduling

Automate workflow execution with cron-based scheduling.

Prerequisites

Start the scheduler process:

dagu scheduler

Or use dagu start-all to run both scheduler and web server.

High Availability

Dagu supports running multiple scheduler instances for high availability with automatic failover:

# Start primary scheduler
dagu scheduler

# Start standby schedulers (on other machines)
dagu scheduler  # Will wait for lock and take over if primary fails

The scheduler uses directory-based locking to ensure only one instance is active at a time. When the primary scheduler fails, a standby automatically takes over within 30 seconds.

The first scheduler updates the lock file every 7 seconds to ensure it remains the active instance, tolerating 4 missed updates before considering the lock stale. This allows a standby scheduler to take over if the primary fails.

Health Check Monitoring

The scheduler provides an optional HTTP health check endpoint for monitoring:

# config.yaml
scheduler:
  port: 8090  # Health check port (set to 0 to disable)

When enabled, access the health endpoint at http://localhost:8090/health.

Note: The health check only runs when using dagu scheduler directly, not with dagu start-all.

Zombie Detection

The scheduler automatically detects and cleans up "zombie" DAG runs - processes marked as running but no longer alive (e.g., due to system crashes or force kills):

# config.yaml
scheduler:
  zombieDetectionInterval: 45s  # Check interval (default: 45s, set to 0 to disable)

When a zombie is detected, its status is automatically updated from "running" to "error". This ensures:

• Accurate status reporting
• Queue slots are freed for new runs
• No manual intervention required

Basic Scheduling

Schedule workflows with cron expressions:

schedule: "0 2 * * *"  # Daily at 2 AM
steps:
  - echo "Processing scheduled task"

Multiple Schedules

Run at different times:

schedule:
  - "0 9 * * MON-FRI"   # Weekdays at 9 AM
  - "0 14 * * SAT,SUN"  # Weekends at 2 PM
steps:
  - echo "Running job"

Timezone Support

Specify timezone with CRON_TZ:

schedule: "CRON_TZ=Asia/Tokyo 0 9 * * *"  # 9 AM Tokyo time

See tz database timezones for valid values.

Start/Stop Schedules

Control long-running processes:

schedule:
  start: "0 8 * * *"   # Start at 8 AM
  stop: "0 18 * * *"   # Stop at 6 PM
steps:
  - echo "Running service"

Multiple start/stop times:

schedule:
  start:
    - "0 0 * * *"    # Midnight
    - "0 12 * * *"   # Noon
  stop:
    - "0 6 * * *"    # 6 AM
    - "0 18 * * *"   # 6 PM

Restart Schedule

Restart workflows periodically:

schedule:
  start: "0 8 * * *"     # Start at 8 AM
  restart: "0 12 * * *"  # Restart at noon
  stop: "0 18 * * *"     # Stop at 6 PM

restartWaitSec: 60  # Wait 60s before restart

Skip Redundant Runs

Prevent overlapping executions:

schedule: "*/5 * * * *"  # Every 5 minutes
skipIfSuccessful: true   # Skip if last run succeeded

steps:
  - echo "Checking status"

Queue Management

Control concurrent executions:

maxActiveRuns: 1  # Only one instance at a time
queue: batch-jobs # Named queue (defaults to DAG name)

schedule: "*/10 * * * *"
steps:
  - echo "Running batch process"

Disable queue processing:

disableQueue: true  # Skip queue, run immediately

Common Patterns

Business Hours Only

schedule: "*/30 8-17 * * MON-FRI"  # Every 30 min, 8AM-5PM weekdays

End of Month

schedule: "0 23 28-31 * *"  # 11 PM on last days of month
preconditions:
  - condition: '[ $(date +%d -d tomorrow) -eq 1 ]'
    expected: "true"

Maintenance Windows

schedule:
  start: "0 2 * * SAT"   # Saturday 2 AM
  stop: "0 4 * * SAT"    # Saturday 4 AM